Place broccoli in well buttered baking dish (9 x 13 x 2).
Melt butter in skillet, add garlic and zucchini, saute for about 5 minutes until zucchini is slightly soft.
Add onions during the last few minutes, adding more butter if necessary.
Place in casserole.
Mix balance of ingredients together and pour over vegetables - stir gently to mix vegetables with sauce.
Sprinkle with extra Parmesan if desired.
Bake uncovered at 325° for 35 to 40 minutes, or until firm in center and slightly browned around the edge